Jet fuel containing anti-wear aromatic diester



United States Patent ()tifice 3,320,041 Patented May 16, 1067 mesne assignments, to Union Oil Company of Califor- 5 nia, Les Angeies, Calif., a corporation of California No Drawing. Filed Sept. 12, 1963, Ser. No. 303,358 16 Claims. (Cl. 44-58) This invention relates to antiwear jet fuel compositions and more particularly to antiwear jet fuel compositions containing a small amount, preferably within the range of about 6 to less than about 50 lbs. per 1000 barrels, of an ester of an aromatic carboxylic acid, preferably an ester of a dibasic aromatic carboxylic acid such as dibutyl phthalate, incorporated in an otherwise conventional jet fuel composition to enhance the antiwear properties thereof under extreme conditions.

It is known in the art that inadequate lubrication frequently causes unusual Wear phenomena in the various sensitive fuel metering and transfer devices of jet aircraft engines. In many of the engine components, the fuel itself must be relied upon to provide lubrication and mitigate wear. While the exact nature of the unusual wear and lack of lubrication is not completely understood, it apparently is related to the high unit pressures developed between parts moving relative to one another, to high temperatures which cause decreases in the viscosity of the fuel and resultant diminished lubricating ability, misalignment of pump gears and other mating parts, localized cavitation where such cavitation induces severe localized mechanical shock on moving parts, etc. It probably is also due in part to the presence of particulate contaminants in the fuel, the particles being introduced into the system with the fuel or being introduced into the fuel within the system through wear, erosion or corrosion. In any event, the many small orifices, valve surfaces and close-tolerance sliding surfaces in the metering devices and fuel pumps are subject to wear because of these conditions, and can be expected to be even more seriously affected as engines of still higher performance are developed in the future.

It has previously been established in the art that the use of various additives and filters may be inadequate to completely overcome these wear phenomena. Further, even 35 sealer.

could become a major problem. It becomes a primary object of this invention to mitigate the problem of wear in various metering, pumping and associated parts used to conduct fuel to a jet engine.

Another object of this invention is to provide a jet fuel composition containing about 6 lbs. of a dibasic aromatic acid ester as herein defined, such as dibutyl phthalate, per 1000 barrels of jet fuel to less than about 50 lbs. per 1000 barrels of jet fuel; that is, in the order of 25 lbs. per 1000 barrels as the upper limit. Still another object of this invention is to provide a jet fuel composition containing about 12.5 to 25 lbs. of dibutyl phthalate per 1000 barrels of jet fuel.

These and other objects of this invention will be described or become apparent as the description thereof proceeds.

In order to demonstrate the invention, a series of radiotracer wear tests was conducted using a gear pump wear apparatus.

Example I tries Model 1203 positive displacement gear pump was used with a capacity of about gallons per hour at 3450 r.p.m. The oil sump was a one-quart glass bottle chosen because it was easy to clean free of wear debris from test to test. The sump was mounted neck down 30 with a sintered steel filter (G.M. diesel injector filter) in the stopper. The fuel line to the pump was attached to the metal screw cap. This sump or container with its filter, outlet line and the fuel charge were analyzed at the end of each run for radiation with a scintillation counter The number of gamma radiation counts in a given period of time is proportional to the amount of iron 59 worn off the gears. In each series of tests, the untreated fuel runs were continued until the apparatus produced essentially constant wear rate results and then the additive fuel runs were made under the same conditions at a concentration of 12.5 lbs. of dibutyl phthalate (DBP) per 1000 barrels of fuel. This order of testing was used to avoid carryover effects of the additive. The sump temperature and fuel appearance were also recorded.

TABLE I.GEAR PUMP WEAR TESTS Base Fuel (JP-4) Additive Fuel Relative 1 Sump Relative 1 Sump Run N0. Wear, Temp, Treatment Wear, Temp,

c.p.m. F. c.p.m. F.

1 52.4 12.5 lb. DBP/1,000 bbl 19.0 2 48.0 12.5 lb. DEF/1,000 bbl 15.2 3 78.8 12.5 lb. DEF/1,000 bbl 3.2 4 39.2

Avg.-. 54.6 12.5 Reduction 2 77 5 12. 7 162 12.511. DB P/LOlINJbbl 8.1 139 11.5 162 12.5 lb. DBP/1,000 bbl 5.9 140 Avg 12.1 7.0 Reduction. a 42 1 In these tests, the wear is presented in radiation counts per minute, which is proportional to the amount of iron 59 in the circulating fluid and to the amount of iron worn from the radioactive pump gears.

2 Percent.

though it is possible to keep the fuel substantially clean, there is evidence that advances in jet engine and aircraft design will result in higher pumping rates and pressures, to the extent that wear of pumps and metering devices From the data, it is seen that reductions in relative wear ranged from 33.4 to 75.6 counts per minute in runs 14, averaging a reduction of 42.1 counts per minute or 77%. Despite mechanical difiiculties in runs 5 and 6 caused by failure of the mechanical coupling between the driving means and the pump, and some leakage at the pump seals, an average relative wear reduction of 42% was realized. Probably of greater interest in the data on runs 5 and 6 is the lower sump temperature in the additive fuel runs; this lower temperature was due to lower heat generation by friction in the pump, thereby further demonstrating the effectiveness of this invention.

Example 11 In a second test, the same irradiated steel gears were used but new seals were installed in the pump. The gear pump was operated for 24 hours at 3450 rpm. and 50 p.s.i. outlet pressure. The operating pressure for the second series of tests was reduced from 150 p.s.i. to 50 p.s.i. in order to reduce the chance of seal leakage Dismantling of the pump to install a new seal was found to change the wear rate and in each instance the pump was run to essentially constant wear rate before DBP was added to the fuel. The gear pump was run on JP-4 fuel without added dibutyl phthalate until consistent wear results were obtained for each run. Then the pump was operated with additive fuel. The results are shown in the following table.

TABLE II.GEAR PUMP WEAR TESTS Base Fuel (II- 4) Additive Fuel Relative Wear, c.p.m.

Relative Wear, c.p.in.

Run No. Treatment 12.5 lb./1,000 bbl 12.5 lb./l,000 bbl... 12.5 lb./l,000 bbl... 12.51b./1,000 bbl 12.5 lb./1,000 bbl...

100 lb /1,000 bbl. 1001b./1,000 bbl--. 100 lb./l,000 bbl.-- 100 lb./1,000 bbl 1001b./1,000 bbl- HM UMAMOO new D-ICOCADOJ Avg Reduction.

1 Percent.

The tests shown in Table II were performed indvidually in consecutive order in accordance with the run numbers. The improvement or wear reduction is seen by a comparison of the averages of the relative wear rates as indicated by the counts per minute of the scintillation counter. At the 12.5 level, an average relative wear reduction of 10.8 c.p.m., or 25.4%, was observed, While at the 100 lb. level the reduction was only 7.6 c.p.m., or 17.4%. However, even though reductions were observed at both additive levels, the results show that all tests run at the 12.5 lb./1000 bbl. level gave a wear reduction While part of the tests run at the 100 lb. level did not show wear reductions. In view of this borderline and uncertain effectiveness at the higher concentration, concentration of DBP is set at less than 100 lb./1000 bbl. of fuel.

Example 111 Following the procedure of Example II, the original, irradiated, steel pump gears were again used for a second series of tests. Each test was run for hours at 3450 rpm. and 150 p.s.i. outlet pressure. The fuel charge of 700 ml. was recirculated, passing through a sintered steel filter at the bottom of the glass reservoir. At the end of the 20 hour period, the amount of wear debris was measured in terms of radiation counts per minute. Each test was performed in consecutive order. in accordance with the assigned run numbers, and the improvement is seen by a comparison of the averages. Larger values for Relative WearC.P.M. were obtained in this series of tests than were obtained in the series under Examples I and 11 because of differences in the counting apparatus arrangement. However, it is ap parent that the individual readings, given in Table III, are consistent within this series, and are significant.

TABLE III.GEAR PUMP WEAR TESTS Base Fuel (IP 1) Additive Fuel Relative Treat- Relative Percent Run No. Wear, Run No. ment 1 Wear, Change from c.p.m. V c.p.m. Base Fuel 802 12.511). 5-59 731 12.5 lb 586 570 12.5lb 524 671 12.5 lb 556 669 9 661 lb 1, 240

1 Lb. DEF/1,000 bbl. Combined average 711.

These results clearly show that dibutyl phthalate in JP-4 fuel still gives a substantial reduction in wear at 12.5 lb./1000 bbl. While concentration of 50 and 100 lb./1000 bbl. increase the wear rate at lb. pump pressure.

In order to establish that the addition of dibutyl phthalate to jet fuel has no deleterious side effects on such critical properties as freezing point, water tolerance and Luminometer number, jet fuel compositions containing 35 lbs. of dibutyl phthalate per 1000 barrels were tested. Table IV shows these properties with and without dibutyl phthalate, the tests on the treated fuel being conducted two weeks after addition of the DBP thereto.

TABLE IV.EFFECTS OF DBP ON JET FUEL Jet Turbine Fuel Without With DBP, Additive 35 lbs/1,000 bbl.

Freezing Point, F 62 62 Water Tolerance, 1111. Change 0. 0 0. 0 Luminometer Number 55 55 Thermal Stability (300/400 F.

Inches Hg pressure drop at 300 minutes 1 0.1 0.1 Preheater tube deposits at 300 minutes 1 Code 0 Code 0 1 Typical.

The JP-4 jet fuel used in the foregoing series of tests exhibited the following characteristics.

5 TABLE V-Continued Gum:

Existent 0.2

Potential 0.4 Freeze point F 86 Aniline point 133.2 API gravity degrees 71.4 Aromatics percent 9.8 Olefins do 0.5 Water reaction (Interface 1) cc 0.5 Smoke point 30.8 Smoke vol. index 68.6

Thermal stability (300/400" F.):

AP, inches Hg at 300 min 0.0

Preheater tube deposits at 300 min Code The physical and chemical limitations of the currently used military and commercial jet turbine fuels are:

TABLE VI.PETR OLEUM HYDR OCARB ONS Gravity, API, 35 min. max 63 Distillation:

I.B.P. F. min" 280 BE F. max 600 Aromatics, vol. percent maX 25 Olefins, vol. percent max 5 Sulfur, wt. percent max 0.4

As is known in the art, there are other specifications for each grade of fuel, such as aniline point, bromine number, gum content, color, etc., which vary somewhat. The above list of properties defines the segment of hydrocarbons suitable for jet fuel.

The additives of this invention may be used to inhibit wear in any jet fuel hydrocarbon composition, which composition will generally qualify as commercial types of jet fuel and also JP1, JP-3, JP-4, JP5, JP-6 fuels and referee fuel as established by the NACA sub-committee on aircraft fuels, now superseded by NASA. The specifications for such jet fuels are described in the Oil and Gas Journal of Oct. 6, 1952, vol. 51, No. 22, p. 96, US. Patent 2,974,025 and specification MILF5624C. The important qualifications are low-temperature fluidity, proper volatility, stability and good odor, and non-corrosiveness to polysulfide-type synthetic rubber parts used in the present fuel systems. Regarding volatility, the military has established that at an atmospheric temperature of 100 F., the minimum 10% A.S.T.M. distillation temperature should be approximately 350 F. Military operations require starting of engines and operations at atmospheric temperatures of -65 F. or lower. At the same time, the engines must operate at high temperatures under conditions where vapor locking, slugging and changes in fuel temperature may occur during flight. Similarly, engine deposits should be at a minimum to prevent decreased performance, poor acceleration characteristics and starter sparkplug fouling. In order to meet safety and performance specifications, the esters of this invention have boiling points greater than about 400 F. Fuels which meet these various specifications are necessarily a compromise of certain qualifications in view of maximum availability from present resources and any mixture of hydrocarbons qualifying as a jet fuel can be used in accordance with this invention.

In addition, the jet fuel hydrocarbon compositions prepared from heavy petroleum fractions such as reduced crudes, gas oils or catalytic cycle stocks or mixtures thereof, as described in US. Patent 2,956,002 of Hillis 0. Folkins, may be used. The compositions of this invention may contain other additives to impart desired properties thereto.

The dibasic aromatic acid ester antiwear agent of this invention has the formula COOR COOR

wherein the COOR groups are in ortho or para position, thus being esters of phthalic and terephthalic acid wherein R and R are C to C straight-chain alkyl radicals, C to C branched chain alkyl radicals, C to C secondary alkyl (iso) radicals, and C to C cycloaliphatic radicals, all containing only the elements carbon and hydrogen and containing no olefinic or acetylenic bonds. R and R may be the same or different radicals such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, isohexyl, heptyl, isoheptyl, octyl, isooctyl, nonyl, isononyl, decyl and isodecyl radicals and cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl radicals. A preferred group of dibasic aromatic esters comprises dimethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diisooctyl phthalate, di-Z-ethylhexyl phthalate, isooctyl isodecyl phthalate, diisodecyl phthalate, butylisodecyl phthalate, butyl octyl phthalate, butyl cyclohexyl phthalate, n-octyl n-decyl phthalate, diisodecyl phthalate, n-octyl n-decyl phthalate, diisodecyl phthalate, and the corresponding terephthalates. Since all of these species may not give equivalent wear rate reduction results, the preferred species is dibutyl phthalate.

Accordingly, this invention relates to jet fuel compositions containing about 10 to less than 50 lbs. of dibutyl phthalate per 1000 barrels of jet fuel and the method of operating a jet engine using such a composition. This invention relates particularly to jet fuel compositions con taining about 10 to 25 lbs. of DBP per 1000 bbls. of fuel and a feature of this invention is the discovery that about 12.5 lbs. of DBP per 1000 bbls. give significant wear reduction.

The DBP may be used in the fuel composition as fed to the jet engine or may be separately injected into the fuel prior to its entry into the jet engine metering system. Thus, the additive of this invention may be used intermittently, if desired, to overcome wear in the metering system during periods of peak loads or where demands of maximum power are required of the jet engines. The various types of metering systems and the wear problem overcome by this invention are described in the prior art, e.g., S.A.E. Booklet 345C entitled, Trans-Canadas Experience with the Rolls-Royce Conway Turbine Engine, by P. T. Dyment and J. 1. Eden; S.A.E. Booklet 47T entitled, Can We Define Aircraft Turbine Fuel Cleanliness Requirements, presented by G. T. Cohn et al. at the S.A.E. National Aeronautic Meeting March 31- April 3, 1959; and S.A.E. Booklet 47S entitled, Orenda Engine Experience with Service Fuels, presented by A. L. Sulton at meeting supra.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A jet fuel oil composition containing metal wearreducing amounts of a dibasic aromatic ester of the formula COOR COOR

wherein the COOR group is in a position other than meta to the COOR group and R and R are of the group consisting of C -C alkyl radicals, C C branched chain alkyl radicals, C C secondary alkyl radicals, and C -C cycloaliphatic radicals, said wear reducing amount being about 6 to less than 50 pounds of said ester per 1000 barrels of said fuel.

2. A jet fuel composition in accordance with claim 1 in which said wear-reducing amount is about to about 25 lbs. per 1000 barrels of said fuel.

3. A jet fuel composition in accordance with claim 1 in which said wear-reducing amount is about 12.5 lbs. per 1000 barrels of said fuel.

4. The method of operating a jet engine and mitigating Wear of metal parts in the fuel metering system thereof which comprises introducing into said metering system the composition of claim 1.

5. A jet fuel oil composition containing about 6 to less than 50 lbs. dibutyl phthalate per 1000 barrels of jet fuel.

6. A jet fuel oil consisting essentially of a jet fuel hydrocarbon mixture and about 10 to about 25 lbs. dibutyl phthalate per 1000 barrels.

7. A jet fuel oil composition consisting essentially of a jet fuel hydrocarbon mixture and about 12.5 lbs. of dibutyl phthalate per 1000 barrels of said fuel.

8. The method of operating a jet engine and mitigating wear of metallic parts in the fuel metering system thereof which comprises introducing into said metering system a jet fuel oil composition containing about 6 to less than 50 lbs. of dibutyl phthalate per 1000 barrels of said fuel.

9. The method in accordance with claim 8 in which said jet fuel contains about 10 to 25 lbs. of dibutyl phthalate per 1000 barrels of said fuel.

10. The method in accordance with claim 8 in which said jet fuel contains about 12.5 lbs. of dibutyl phthalate per 1000 :barrels of said fuel.

11. The method in accordance with claim 8 in which said jet fuel composition is introduced into said metering system at periods of peak load in said system for the operation of said jet engine.

12. The method of operating a jet engine and mitigating Wear of metallic parts in the fuel metering system thereof which comprises introducing wear-reducing amounts of dibutyl phthalate into the fuel entering said metering system.

13. The method in accordance with claim 12 in which said dibutyl phthalate is introduced at a concentration of about 6 to less than lbs. per 1000 barrels of said jet fuel.

14. The method in accordance With claim 12 in which said dibutyl phthalate is introduced at a concentration of about 10 to 25 lbs. per 1000 barrels of said jet fuel.

15. The method in accordance with claim 12 in which said dibutyl phthalate is introduced at concentration of about 12.5 lbs. per 1000 barrels of said jet fuel.

16. A jet fuel composition consisting essentially of a hydrocarbon fuel qualifying as a JP-4 jet fuel and about 12.5 lbs. of dibutyl phthalate per 1000 barrels of said fuel.

References Cited by the Examiner UNITED STATES PATENTS 1,980,097 11/1934 Ruddies 4470 X 1,993,737 3/1935 De Witt et al 25257 X 2,158,096 5/1939 Werntz 25257 X 2,215,590 9/1940 Maverick 25257 2,409,444 10/1946 Morgan et al 25257 X FOREIGN PATENTS 432,592 7/1935 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

W. J. SHINE, Assistant Examiner. 

1. A JET FUEL OIL COMPOSITION CONTAINING METAL WEARREDUCING AMOUNT OF A DIBASIC AROMATIC ESTER OF THE FORMUAL 